Process and apparatus for separating granular material



Aug. 18, 1942. 'A A, HlR-r 2,293,340

PROCESS AND APPARATUS FOR SEPARATIMG GRANULAR MATERIAL Filed May 3l, 1940 3 Sheets-Sheet 1 Aug. 18, 1942.

-A. A. `HlFeT 2,293,340

'PROCESS AND APPARATUS FOR SEPARATING GRANULARMATERIAL Filed may s1, 1940 s'sheets-shet z A. A. HIRST Alu- 1s, 1942.

PROCESS AND APPARATUS FOR SEPARATING GRANULAR MATERIAL Filed May 3l, 1940 3 Sheets-Sheet 3 Atta/"nega finely comminuted solid.

1 curved and Patented Aug. 18,y 194.2

i vUNITED a STATES PATENT OFFICE Arthur Algernon Hirst, Northfield, Birmingham,

England, assigner Carves Limited, Cheadle England y one-half to Simon- Heath, Stockport,

Application May 31, 1940, serial No. 338,132

` In Great Britain June 5, 1939 paratus for separation of granular material such as coal or ores, the invention being concerned with a process and'apparatus forseparating materials according -to density involving the use of a separating fluid consisting of a suspension oi' nely comminuted solid in water or other A uuid.'

l Any. suitableA finely Vcomminuted solid may be used, but for convenience in description the term "sand is used hereinafter The primary object of the present invention is to enable morecomplete and accurate separa-y tion of the different products;v so as to minimise the disadvantage or part of one product-being removed with another'product.

A `further object is the provision of means for regulating or `controlling thev points of separation between the various products separated to to include any suchl` rsecured together so that passes down the inlet e d II and-up the outlet end I 2 of the base.

Extending across .the open top of each pocket are shield plates 22 disposed vertically and parallel to thevlength of serving the dual purpose of acting as guides for the s aper `and minimising eddy currents in the t p of the pocket. Such shield plates may be adjustable as regards positions and eiective depth oi?y plate in the pocket and forthis latter purpose each .plate may comprise 'two strips overlapped as shown in Figure 2 and adjustably the extent of overl-apping can be varied.

A cover plate 23 is mounted adjustably upon the base I3 yof the trough adjacent each pocket for movement partially to close the open top of the pocket so that the area of this top can enable adjustment of the products or any one of the products. p

Referring to the drawings-f Figure 1 is anelevation of one apparatus according to this invention.

Figure 2 is a section on line 2-2'01 Figure 1.

Figure -3 isa section on line 3`3 of Figure 2.

Figure 4 is a section on line 4-4 of Figure 1. i Figure 5 4is a perspective view of a detail.

In one construction according .to this invention the apparatus includes an elongated trough or vessel I which isv relatively shallow, the b ase of the-trough being inclined atfthe two ends,

v namely, the inlet end as indicated at Il andthe outlet end as indicated at I2 in Figure 3, whilst at the centre of the length of the trough and intermediate these ends the base I3 is slightly may if desired be flat and horizontal.

l In theV part I3 oi the 'base `there are two pockets I4 and I5 each of which extends acrossthe andlforms a decompletewidth of the trough pression in the baseof the trough.

Extending through the trough inthe direce tion of the length thereof is an endless scraper I6 comprisingscraping bladeslklof substantial-` ly U shape pivoted together on link pins I8 as `indicated in `Figure 5, vthe, ends of the sides' of the U shaped bladesbeing out-turnedy at Iy to scrape the sides of the trough and prevent, de-

posits or accumulationslsuchas might ytend to` impede theloperation' of the scraper.'` ,j

dtrotata'bly supported at -thentwo en'ds. 0f I15h@ befvaried as required ornecessary.

Each pocket is provided with extensions 24 and 25 leading upwardly from opposite sides oi.I`

side of the trough as the pocket, one on either indicated in Figure `2, the extension 24 being vertical and parallel to the depth of the trough,.,

whilst the extension 25 is inclined at an acute angle to the' depth of the trough and pocket.

Each pocket is provided with a mechanical scraper 26 for removing from the pocket any material sinking or deposited therein, each scraper. passing over carrying Amembers 21 suitably mounted on the supporting structure and driven from the drive means for the apparatus;

The scraper passes downwardly in the extension 24 `and upwardly over the inclined base of the extension 25 so that materialv deposited in the pocket is removed up this inclined base.

Y Each scraper 26 may be constructed `substantially as described and illustrated in the case oi' .the scraper lli.v i Y A pair of vertical plates` y28 for each pocket VAform uadjustable baiiles one at .each-side of each pocket, these plates lbeing v slidable vertically by .the operation of control rods 29 so 'that Athe l This' scraperyis mounted on carrying `members y trough being driven by a` .drive 2| from lthe A drive` means for thevapparatus. Thetlower run off the chain movesover the base of lthe .trough liforwthe complete length of the latterjthe direcftionof movement Kpeing such J that the "chain depth of cross'flow `acrossthe.. pocket vfrom the extensions 24 andv25 can beregulated.' 'A

"A transverse partitiony 30 is mounted 'in-the trough intermediate the ends thereof, this partition extending completely across the width of the trough v:for a depthV less than thatof the trough at' the position of Athe partition. This partition'comprises two plates `placed one upon `the other tooverlap `and secured together in a manner permitting variation of the extent of overlapping' so` that the eiective depth `of the partition in 'the trugh-canbeadjusted.

At the in let end of the trough there is atrans- 'verse channel -31 extending across the width of Vthe trough" and provided with an inclined baille 32.` the elective the trough, suchplates v depth A0f which in Ythe 'trough i can be regulated as described in the case of the partition 30.

Circulating through the trough is a separating fluid comprising a suspension of sand in water or other fluid, the density of the suspension being maintained substantially constant as will hereinafter be described.

At the outlet end I2 of the trough there is an adjustable plate 33 mounted for movement over the end of the inclined portion I2 of the base enabling variation of the effective height of the outlet over which is discharged the material removed by the scraper I6. L

Similarly an adjustable plate 33 is mounted at the upperlend of the inclined base of the extension 25 of each pocket to enable variation of the effective height of the outlet over which is dis-v charged material removed from the pocket by the mechanical scraper therefor.

Such material removed from the pocket falls upon a perforated screen or jigger 34 shown in Figure 2 and upon the first portion of this screen the material is drained of suspension which is collected in a cone 35, whilst on a further portion the material is sprayed or washed by discharge of liquid from sprays 36, such spray liquid being collected in a cone 31 whilst the washed material is discharged down a chute 38.

This arrangement is duplicated for each of the pockets I4 and I5 and for the material discharged from the outlet end of the trough.

Above the trough is a chute 39 down which is discharged the material to be treated in the apparatus, this material falling into a horizontal channel 4I) along which passes the upper run of the scraper I6 which thus operates to move the material along the channel 40 to a further inclined chute 4I leading down into the trough in advance of the partition 30.

In advance of the chute 4I is a comb conveyor 42 mounted on sprockets 43 and driven from the drive means for the apparatus, the rotation of this conveyor being such that the lower run, which dips into the liquid in the trough, tends to engage the product floating in the suspension and to move this product over the baiile 32 and into the channel 3I.

This material falls on a perforated screen or jigger 44 and is drained of suspension whilst on the portion of the jigger extending in the transverse channel 3|, whilst on a further portion of the jigger the material is washed by discharge from the sprays 45, the spray liquid being collected in a cone 46 whilst the washed material is discharged down a chute 41.

For maintaining substantially constant the density of the suspension in the trough I this suspension is circulated between the trough and a reserve tank 48 shown in Figure 1, the suspension being pumped from the tank through a pipe 49 in which is a pump 5I) and which discharges into. the inlet end of the trough.

The suspension removed from the trough by the operation of the scrapers I6 and 26 is drained from the separated products as above described and this suspension is conveyed back to the reserve tank from the collecting cones 35 and the channel 3I by means of pipes 5I.

Intimate mixing of the suspension in the re' serve tank 48 is ensured by circulating the suspension Within the tank by a circulation pipe 52 in which is a pump 53 and which withdraws suspension from the base of the reserve tank and discharges such suspension into the top of the tank.

The underflow from the collecting cones 31 and 46, namely, the spray medium collected after spraying the separated products, is conveyed by pipes 54 to a dilute suspension tank 55 in the top of which is a fine mesh screen or jigger 56 for rseparating the liquid from the slurry washed from the separated products by the sprays, such slurry being again sprayed on this screen 56 from sprays 51 and being then discharged down a chute 58.

The under flow from the dilute suspension tank is forced by a pump 59 through a pipe 60 to a settling tank 6I having an overflow rim 62 from whichI clear suspension is passed back to the reserve tank through a pipe 63, through a density control device 60 for mixing clarified overflow and thickened underflow from the tank 5I, whilst an overflow pipe 64 leads from the top of this rim down to a spray medium tank 65 feeding the sprays 36, 45 and 51 through a pipe 66 provided with a pump 61.

The base of the settling tank 6I is connected by a pipe 68 to the reserve tank 48 and in this pipe 68 is a valve 69 and the density control device 60.

Referring to Figure 2 a pipe 1I in which is a pump 12 connects the pocket extensions 24 and 25, the inlet end of the pipe being below the level of suspension in the corresponding extension but the outer end not necessarily being below the level in the corresponding extension. This pipe 1I communicates through a two-way valve 13 with a pipe 14 leading to the reserve tank 48.

By operation of the pump 12 for either pocket, suspension can be circulated between the extensions 24 and 25 to ensure a desired cross flow across the main part of the pocket or to compensate or the effect of the movement of the scraper 26 through the pocket, whilst by means of the bye-pass pipe 14 suspension can be withdrawn at a controlled rate from the pocket and discharged into the reserve tank.

The pipe 14 can be used even if the circulating pipe 1I and pump 12 are omitted.

An overflow 15 from the reserve tank leads into the tank 55.

In operation the material to be treated, for example the coal to be washed or cleaned, is fed down the chute 39 and is moved by the scraper I6 to the chute 4 I, being discharged thereby into the trough on the inlet side of the partition 30.

For separating coal particles from dirt or foreign matter the specic gravity of the separating uid may be regulated at a figure of about 1.35, i. e., at a density equal to that at which clean coal flows through the body of the separating fluid to collect at the top of this fluid whilst the dirt or middlings sink in, or remain suspended in, the fluid.

The clean coal flowing in the fluid is moved by the comb conveyor over the partition 32 and on to thescreen 44 where the coal is first drained of suspension and is then sprayed prior to being discharged down the clean coal chute 41.

Material falling through the separating fluid is carried by the scraper I6 over the first pocket I4 and the heaviest material falls into this pocket and is given a further separation treatment therein.

The specific gravity of the suspension in the rst pocket I4, is, for example, maintained at a figure of 1.8 as will be referred to later herein and the particles of heavy dirt fall to the bottom of the pocket, whilst lighter dirt or middlinzs trough and arranged in the by thescraper l |61 Material not heavy Venough to "fall into the pocket I4 is carried pension is maintained at a gure of 1.5 andn again the material isfseparated into a heavy product on` bythe scraper tofthe pocket l5 where the specific gravity of the sustrolled outlet arrangement the of opening of the outlet similarly controls the fallingin the pocket to the base thereof and lighter material floating in the pocket.A

The productjfalling to thevbase of each pocket is removed from the pocket by' the'scraper 26 and is dischargedon'to the screen 34 for the particular pocketbeing drained clear of suspension and then sprayed prior to discharge down the chute 38.

Material retained by the scraper after passing over the top of the pocket I4 is moved up the inclined portion l2 of the base of the trough and is discharged over the outlet 33 on to the screenl where it is drained and sprayed prior to discharge down the appropriate chute.

The pockets or zones containing suspension of greater density than that in the main separating base of this trough may be likened to U tubes, one limb of which communicates with the main trough, whilst the other limb is open to theatmosphere. Since the suspension in the pocket is denser than that'in the main trough it is clear that for conditions of equilibrium the level of the suspension in the limb of the pocket communicating with the atmosphere, i. e., in the pocket extensions 24 and 25, must be lower than the level lof suspension in the main trough. l

It follows that the suspension in the pocket must not be allowed to overiiow freely at this lower level otherwise suspension would flow into theV pocket'from the main trough, thereby tending to reduce the density of the suspension in the pocket to that of the suspension in the main trough.

On the other hand, if there is no outlet whatsoever for thefsuspension and, if any, settled sand from the pocket,` the suspension in the pocket will tend `to consolidate and cause the pocket to become choked with settled sand.

In order to maintain, in the pocket, a suspension with a density greater than that in the main trough whilst avoiding this sary to withdraw suspension and settled sand from the pocket in controlled amounts.

According to the present invention this l'is effected in. one or both of two ways.

'I'he iirst is by providing a controlled outlet for suspension and settled sand in the pocket or the'limb communicating therewith' at a level below the surface of the suspension in the limb communicating with the atmosphere.

choking, it is neces-v The second is to design the means for withdrawing the particles sinking into the pocket so that in addition to such particles suspension and settled sand may also beevacuated in controlled quantities.

In the latter case the control of the removal of suspension and settled sand is effected by variations in the formof the scraper, or by varying its speed. f

In general the density of the suspension in the pocket will be greater or less according` as the quantity of suspension and settled said removed isless or greater respectively.

The suspension and settled sand are` removed from the pocket at a levelv below that of the separating uid in the tank as distinct from a mere Vco overflow leading from the pocket. i

With anv endless or other scraper for removing the suspension, settled sand and material sink-` `area of the lower portion or ing in the suspension from the pocket, the form and speed of' operation rateof removal of lsuspension and settled sand and thus control the' electivedensity of the material remaining in the pocket, whilst with a coneXt'ent and period rangement the materialsinking in the suspension type scraper, i. e., one provided with hollow or.'

bucket-type blades, lwhilst the scraper in afurther pocket may be provided with flat blades so that the amount* of suspension or settled sand removed from the two pockets will be diierent and accordingly the density of the suspension in the two pockets will be different.

For evacuating the suspension, settled sand and separated material from a pocket a mechanical scraper or ,similar device is preferred toa bucket elevator. l

A scraper can be arranged to sweep the whole settling zone of a shallow pocket, whereas a bucket elevator requires atapered inlet and elevator boot, thus increasing the eiective depth of the pocket; It :is leasier to maintain a suspension of substantially uniform density in a shallow pocket than in one of greater depth. Moreover a scraper tends to maintain to some extent a condition of uniform density in the pocket since if the densityof the suspension increases the viscosity of the suspension and the quantity cf settled sand both increase so that a greater quantity of suspension or settled sand adheres to the scraper and is evacuated, bringing about a reduction in the density of the suspension.

If the density of the suspension increases, the viscosity of the suspension and the quantity of settled sand decrease so that a smaller quantity of suspension and settled sand is evacuated, consequently the density of the suspension tends-to increase.` Also when a mechanical scraper is used it is possible to control the quantity of suspension and settled sand evacuated in a convenient-fashion by means ofthe adjustable plate 33 in the base of the scraper casing at the outlet or delivery end. If this plate is lowered the `quantity of material removed by the scraper is in,

creased whilst if There may be a tendency for the density of the main suspension to fall slightly towards the outlet end of the trough, namely,to a figure of about 1.33 and this facilitates the depositionin the last pocket of material having a density of about 1.35.

The material deposited in ell the pockets can be removed separately and in this way three or` more gradesof heavy material of densities greater than that ofthecl'ean coal, can'be removed sep arately from the apparatus. l y

It will be appreciated. that the ligures given above for the of the scraper controlthe.

gravity ofthe suspension densities in the various parts of' the apparatus are of the pockets may material sinking in said main only included by way of example and the density in the trough and in any be regulated at any convenient ilgure depending upon the materials to be separated and upon the grades of such material desired to be separately collected.

Also, when a reserve tank is connected in circuit with the pocket and its extensions, the suspension and settled sand removed from the lower part of the pocket may be discharged into the reserve tank where the density of the suspension is adjusted to that required for the pocket, by admixing as required suspension of a greater or lesser density; suspension oi the correct density being recirculated back to the pocket. The reserve tank may be provided with an overflow into the reserve tank for the main circulation so that the excess or' suspension withdrawn from the pocket together with any excess suspension produced in adjusting the density of the suspension in the reserve tank is returned to the main circulation; this arrangement also provides a substantially constant circulation in the pocket.

The suspension in a reserve tank for the main circulation or in a reserve tank in circuit with a pocket and its extensions, if any, may be automatically stirred in order to maintain a suspension cf uniform density.

The circulation in the or each pocket can be maintained by means of one or more air lifts, or the scraping device can be arranged to produce a circulation, but it is preferable to use a pump or the like for the main circulation.

What I claim is:

1. A process for separating granular material involving the steps of introducing the material to be treated into a main body of separating fluid, such main body being ribbon-like or shallow in relation to its length and being of substantially constant density throughout, subjecting said material to a primary separation treatment in said main body of fluid, removing the granular material floating in said main body, subjecting the body of separating fluid to a, secondary separation treatment in a pocket of separating fluid projecting downwardly from the underside of said main body and extending for a relatively short distance along the length of said main body, the density of said pocket of separating iluid being substantially constant throughout and being greater. than the density of the main body of separating fluid, maintaining the density of said pocketsubstantially constant by removing material from the pocket in a controlled manner, returning into the main body of separating fluid the material floating from said pocket, removing said last mentioned floating material separately of the material floating in said main body, and removing separately the material sinking in said pocket.

2. A process for separating granular material involving the steps of introducing the material to be treated into a main body of separating fluid, such main body being ribbon-like or shallow in relation to its length and being of substantially constant density throughout, subjecting said material to a primary separation treatment in said main body of fluid, removing the granular material floating in said main body, subjecting the material sinking in said main body of separating iluid to a secondary separation treatment in a plurality of pockets of separating fluid projecting downwardly from the underside of said main body, each of said pockets extending for a relatively short distance along the length of said main body, the density of each of said pockets of separating fluid being substantially constant throughout and being greater than the density of the main body of separating fluid, maintaining the' density of each of said pockets substantially constant by removing material from the pocket in a controlled manner, introducing said sinking material ilrst into a pocket o'f maxlmum density, returning into the main body of separating fluid the material floating from said pocket, introducing said last mentioned floating material into a further pocket of density less than that of the first mentioned pocket but greater than that of the main body of separating fluid. returning into the main body of separating fluid the material floating from said further pocket, removing said last mentioned floating material separately of the material floating in said main body, and removing separately the material sinking in said pockets.

3. A process for separating granular material according to claim 1, involving the removal from said pocket in controlled amounts of settled sand together with separating fluidfor maintaining the density of said pocket substantially constant.

4. Apparatus for separating granular material including an elongated vessel shallow in relation to its length, said ves'sel containing a separating fluid of substantially constant density throughout and consisting of a suspension of finely comminuted solid, a pocket projecting downwardly from the base of said vessel and extending for a short distance along the length of the base, said pocket containing a suspension the density of which is maintained substantially constant throughout at a figure greater than thatof the main body of separating fluid, means for removing the granular material oating inA said main body, means for moving to said pocket any material sinking in said vessel so as to subject such material to a further separation in said pocket, an extension on each of two opposite sides of said pocket each extension communicating with, and

projecting upwardly from, the bottomV of the pocket to a height above the levelfof fluid in the said vessel, a mechanical conveyorv for said pocket, said conveyor passing down one extension of the pocket across the bottom of the pocket and up the other extension of the pocket for removing the material sinking in the said pocket and means for removing the material floating from said pocket but sinking in the main body of fluid, said last mentioned material being removed separatelyof the material floating in the main body of fluid and separately of the material sinking in said pocket.

5. Apparatus according to claim 4 including means for circulating suspension in said pocket between the extensions thereof by withdrawing suspension in controlled amounts from one extension and discharging such withdrawn Asuspension into the other extension of the pocket.

6. Apparatus for separating granular material including an elongated vessel shallow in relation to its length, said Vessel containing a, separating fluid of substantially constant density throughout and consisting of a suspension of finely comminuted solid, a pocket projecting downwardly from the base of said vessel and extending for a short distance along the length of the base, said pocket containing a suspension the density of which is maintained substantially constant throughout at a figure greater than that of the main body of separating fluid, means for removing the granular material floating in said main t body, t material sinking in said vessel so as to subject j without. an overow,

means for moving to said pocket any such material to a further separation in said pocket, an extension on each of two opposite sides of said pocket each extension communicating with, and projecting upwardly from, the bottom of the pocket to a height above the level of lluid in the said vessel, the suspension in said extensions having a free surface with the atmosphere an endless link scraper conveyor for said pocket said conveyor passing down one extension of the pocket across the bottom of the pocket horizontally and transversely of the length of the vessel and up the other extension of the pocket for removing the material sinking in said pocket and means for removing the material floating from said pocket but sinking in the main body of uid, said last mentioned material being removed separately of l the material floating in the main bodyof iiuid and separately of pocket.

7. Apparatus according to claim 4 including controllable means for varying the strength of the cross flow in said pocket between the extensions thereof.

8. Apparatus for separating granular material including an elongated vessel shallow in relation to its length,V said vessel containing a separating uid of substantially constant density throughout and consisting of a suspension of finely comminuted solid, a pocket projecting downwardly from the base of said vessel and extending for a short distance along the length of the base, said pocket containing a suspension the densityA of which `is maintained substantially constant throughout at a gure greater than that of the main body of separating iiuid, means for removing the granular material oating in said main body, means for moving to said pocket any material sinking in said vessel so as to subject such material to a further separation in said pocket, an extension on each of two opposite sides of said pocket, each extension communicating with, and projecting upwardly from, the bottom of the pocket to a height above the level of fluid in the the material sinking in said 4 said vessel, the suspension in said extensions having a free surface with the atmosphere without an overow, an endless link scraper conveyor for said pocket, said conveyor passing down one extension of the pocket across'the bottom of the pocket horizontally and transversely of the length of the 'vessel and up-the other extension of the pocket for removing the material sinking in said pocket, adjustable means for controlling tlie area of the openings between the pocket and its extensions for regulating the strength of the cross flow in said pocket between said extensions and means for removing the material floating from said pocket but sinking in the main body of fluid said last mentioned material lbeing removed separately of the material floating in the main body of iluid and separately of the material sinking in said pocket.

.9. Apparatus for separating granular vmaterial including an elongated vessel shallow in relation to its length, said vessel containing a main body of separating iiuid of substantially 'constant density throughout and consisting of a suspension of iinely comminuted solid, a plurality of pockets at spaced positions along the length of said ves- 5 sel, each of said pockets projecting downwardly from the base of the vessel and extending for a short distance along the length of the base, each pocket containing a suspension of density substantially constant throughout and greater than that of the main body of iluid, means for moving to the first of said pockets the material sinking in said vessel, means for moving thematerial floating from said first pocket to a further pocket containing separating fluid of density less than that of the fluid in the first pocket but greater than that of the main body of iluid in the vessel. an extension on each of two opposite sides of each of said pockets each extension communicating with, and projecting upwardly from, the bottom of the pocket to a height above the level of iiuid in the said vessel, a mechanical conveyor for each of said pockets, said conveyor passing down one extension of the pocket across the bottom of the pocket and up the other extension of the pocket for removing the material sinking in said pocket and means for removing the material lloating from said further pocket but sinking in the main body of fluid, said last mentioned material being removed separately of the material floating in the main body of iluid and separately of the material sinking in said pockets.

10. Apparatus for separating granular material including an elongated vessel shallow in relation to its length, said vessel of separating fluid of substantially constant density throughout and consisting of a suspension of finely comminuted solid, a plurality of pockets at spaced positions along the length of said vessel, each of said pockets projecting downwardly from the base of thevessel and extending for a short distance along the length of the base, each pocket containing a suspension of density substantially constant throughout and greater than that of the main body of fluid, an endless lint; scraper moving along the 4base of the vessel ror moving to the first of said pockets the material height above the level of fluid in the said vessel,.

the suspension in said extensions having a free surface with the atmosphere without an overflow, a mechanical conveyor for each of said pockets, said conveyor passing down one extension of the pocket across the bottom of the pocket horizontally and transversely of the length of the vessel and up the other extension of the pocket for removing the material adjustable means for each pocket for controlling the area of the openings between the pocket and its extensions for regulating the strength of the cross ow in said pocket between said extensions, and said endless scraper removing the material floating from said further pocket but sinking in the main body of uid, said last mentioned material being removed separately of the material oating in the main body of iiuid and separately of the material sinking in said pockets.

ARTHUR A. HIRST.

containing a main body sinking in said pocket, 

